Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$97.81	13.792%	$111.3	$111.30	$111.30	$111.30
Purchase #2	$127.72	10.397%	$140.999	$141.00	$141.00	$141.00
Purchase #3	$222.61	5.217%	$234.2236	$234.22	$234.20	$234.20
Purchase #4	$64.81	4.433%	$67.683	$67.68	$67.70	$67.70
Purchase #5	$117.31	9.564%	$128.5295	$128.53	$128.55	$128.50
Purchase #6	$24.47	5.658%	$25.8545	$25.85	$25.85	$25.90
Purchase #7	$127.77	4.268%	$133.2232	$133.22	$133.20	$133.20
7 purchase totals =	$782.50		$841.8128	$841.80	$841.80	$841.80